The present invention relates to a rod-bed assembly and to be more precise to a rod-bed assembly for a rod of a device for coating or sizing a fiber web, particularly a paper or a board web. The invention also relates to a rod—rod-bed assembly.
In this description and in the claims, by term rod-bed assembly is meant the rod-bed comprising an insert and a holder for a rod of a device for coating or sizing a fiber web. The front side of a rod-bed assembly is the side on which the rod is located in use i.e. the side that will face the fiber web to be coated or the sizing roll onto which the sizing agent is applied by the rod when sized. It should be understood that in the prior art publications relating to rod-bed assemblies there exists differences in the terminology used, for example in relation to the feature whether or not the rod is included in the assembly. In practice the rods and the rod-bed assemblies can be supplied to a device for coating or sizing a fiber web from different suppliers or from the same supplier.
As known from the prior art in fiber web producing processes, the fiber web producing processes typically comprise an assembly formed by a number of apparatuses arranged consecutively in a process line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a sizer, a calender, or a coating section. The production and treatment line also comprises at least one winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by fiber webs are meant for example paper and board webs.
In production of fiber webs, for example of paper or board webs, sizing is used to alter the properties of a fiber web by adding sizing agents (sizing medium), for example glue chemicals. Sizing can be divided to internal sizing and surface sizing. In internal sizing the sizing agent is added to pulp in the wet end of the fiber web machine before forming. In surface sizing the sizing agent is added onto the surface of the fiber web at the dry end of the fiber web machine.
In production of fiber webs, for example of paper or board webs, a coating, especially of the surface of a fiber web is formed with a layer of coating paste (coating medium) at a coating station followed by drying. The coating process can be divided in supplying the coating paste onto the web surface, which is called the application of the coating paste, as well as in the adjustment of the final amount of coating paste.
The coating or the sizing of a fiber web typically utilizes a coating device—a coater—or a sizing device—a sizer. In connection with the coaters and sizers, different kinds of application technology for application of the coating or the sizing medium on the fiber web are employed in prior art arrangements, for example curtain technology or blade coating technology or rod coating technology or air brush coating technology or spray coating technology.
In the coating or sizing based on rod technology rod-bed assemblies are used for the rod or doctor rod functioning as dosing element of the coating or sizing medium, for scraping off the excessive medium quantity, of the sizing or coating medium. In the sizing the rod functions against a roll and in the coating the rod functions against the fiber web.
DE 100 45 515 A1 shows one example of a known rod-bed assembly which comprises a holder, a doctor bed made of elastic material inserted into the holder for rods with diameter less than 25 mm and in which the cross section surface of the rod-bed is less than three times the cross section of the doctor rod.
EP 1 485 209 A1 shows a further example of a known rod-bed assembly in which a metal doctor rod that has a diameter less than 25 mm is insertable into a rod-bed made of elastomer. The rod-bed insert is inserted into a holding groove of a holder also made of elastomer.
EP 1 954 880 A1 shows yet a further example of a known rod-bed assembly in which the rod cradle (the rod-bed) includes a frame profile (holder) equipped with an insert groove, an insert fitted to this equipped with a rod groove, and a rod and locking elements for locking the insert into the frame profile. This known rod-bed assembly is for rods with a diameter of 9-25 mm.
WO 2010/142513 shows also an example of a known rod-bed assembly comprising a holder made of composite material, a rod-bed made of polymer and a o doctor rod rotatably supported in a bearing recess on the front side of the rod-bed.
The holder is formed such that the rod-bed and the doctor rod are insertable into and removable from a socket provided in the holder in the radial direction of the rod and the rod-bed comprises closed cavities for saving material. This known rod-bed assembly mentions as large rods doctor rods having a diameter of 20 to 25 mm and requiring larger rod-beds and holders.
It is a problem of prior art that the rod-bed assemblies are not suitable in cases where rods of diameter over 25 mm are used since space requirements for inserts of rod-bed assemblies that would be suitable for larger rods (i.e. rods with diameter over 25 mm) cannot be realized due to lacking space for locking surfaces, cavities etc. of these known assemblies.